I don't think I've seen this before. Does it also happen when running the following script? Can you
upload the video and I'll try to reproduce the issue?
Code:
import viz
import vizact
viz.go()
quad = viz.addTexQuad(pos=[0,1.8,3])
video = viz.addVideo('video.mp4')
video.play()
quad.texture(video)
vizact.onkeydown('1',video.setTime,0)
vizact.onkeydown('2',video.setTime,30)
vizact.onkeydown('3',video.setTime,60)
vizact.onkeydown('4',video.setTime,90)
vizact.onkeydown('5',video.setTime,120)
vizact.onkeydown('6',video.setTime,150)